1. Field of the Invention
The present invention relates to hard disk file storage systems. More particularly, the present invention relates to a disk drive in a hard disk file data storage system.
2. Description of the Prior Art
Disk file data storage systems contain one or more magnetic disks on which data is stored in sectors which lie in concentric tracks on the disks. A transducer (or head) flies above a track and writes, or magnetically encodes, the data in a sector on the track. The head is also capable of reading the magnetically encoded data from the sectors.
An electromechanical actuator operates within a negative feedback, closed-loop servo system. The actuator moves the head radially for track seek operations and holds the transducer directly over a track for track following operations.
Typically, a file of disks is stacked on a spindle. Each surface on each magnetic disk has one corresponding head. All heads are moved together by the electromechanical actuator to different tracks on the disk surface. The collection of the tracks under all heads at any given radial position along the disk file is known as a cylinder. Data read from the sectors by the heads is demodulated in a disk drive interface and provided to a host computer.
In the past, serial or classical disk drive interfaces, such as the ESDI or ST506 interfaces demodulated the data read from the track on the magnetic disk and provided it in serial form. An additional component, known as a disk drive controller, checked the integrity of the data provided by the serial disk drive interface and converted the serial flow of data into a parallel flow. The parallel information was then provided by the disk drive controller to a host computer.
More recently, disk drive interfaces have been designed with more intelligence than the classical or serial disk drive interfaces. Examples of such intelligent disk drive interfaces are the SCSI and PCAT (which was invented based on the PC-AT computer design) interfaces. Functionally, these intelligent interfaces and the disk drive controller have become part of the disk drive and provide parallel data to the host computer
Most PC-AT type host computers are programmed to operate with a number of specific disk drive types. The PC-AT type host computer contains a table of disk drive types which it will operate with. That table contains the number of cylinders, heads and sectors per track for each drive type entered in the table. This table is fixed in the Basic Input/Output System (BIOS) ROM.
A power up program located in the BIOS ROM provides the disk drive controller with the disk drive parameters, from the table, which correspond to the drive type that the host computer is programmed for. The disk drive controller then configures itself to match the table entry corresponding to the disk drive parameters provided by the power up program.
All disk drive types included in the table in the PC-AT type computer use a sector number of 17 sectors per track with a specific number of heads and cylinders.
The fixed table imposes a limitation on the maximum disk drive capacity that the lost computer can access. This is an increasing problem with the advances being made in enlarging disk capacity.
The computer typically addresses the disk drive through BIOS calls. Presently, typical BIOS programs allow up to 1024 cylinders, 16 heads and 64 sectors per track to be addressed Hence, the maximum disk drive capacity addressable by BIOS is 1,048,576 blocks (536,870,912 bytes). But, if the computer cannot address more than 17 sectors per track because of the inflexible disk drive type table, the addressable disk drive capacity is cut down to 278,528 blocks (142,606,336 bytes).